Stem cells hold the promise of a therapeutic approach for treating disease, the control of tissue regeneration, the delivery of therapeutic agents and potential for replacement of a diseased cell population. However, manipulation of stem cells can only be achieved by understanding how they are regulated. It is increasingly evident that this regulation is achieved by environmental cues emanating from their specialized environment (niche). While many signaling pathways influence stem cell activity, beta-catenin signaling profoundly impacts the stem cell fate, inducing divergent cellular responses when induced or ablated. Recently, we have shown that during intestinal development over-expressing Wnt/beta-catenin signaling in the stem cell niche impacts the stem cell's proliferative capacity. Based on this data we believe that the Wnt/beta-catenin signaling pathway plays an important role in establishing the developing intestinal stem cell niche and maintaining the mature niche in the adult. The goal of this study is to test the hypothesis that Wnt/beta-catenin signaling is organized in a temporal manner to establish the intestinal stem cell niche and in a spatial manner for maintenance of the proliferation-to-differentiation progression within the mature niche. To test this hypothesis we will use Wnt-reporter and DNTcf-4 expressing mice (ablated Wnt/beta-catenin signaling) to characterize the temporal and spatial expression pattern of Wnt/beta-catenin activity during the stem cell niche morphogenesis and adulthood. Additionally we will determine if spatial expression of Wnt/beta-catenin signaling is required to maintain the adult stem cell niche by dissecting and analyzing discrete cell strata within the niche. Disruption of the normal expression of Wnt/beta-catenin by induction of a beta-catenin signaling molecule or a DNTcf-4 molecule will determine the dependence of signaling upon crypt establishment and maintenance. Finally, DNA microarray analysis will identify global changes in gene expression between the cellular regions of the developing stem cell niche (wild-type and DNTcf-4 intestines) to directly determine the role of Wnt/beta-catenin signaling on stimulation of molecules and pathways. These proposed studies will directly examine the role of Wnt/beta-catenin signaling on maintenance of the stem cell niche and will shed insight into the regulatory control of intestinal stem cells.